Carbon Isotope Values Research Articles

Distinguishing West Florida gag (Mycteroperca microlepis) nurseries with otolith stable isotopes

Numerous reef fishes utilize estuarine nurseries following spawning in marine habitats. Nursery origin affects their life cycle space use, and otolith chemistry can be an effective tool for tracking movement over this lifetime scale. Gag Mycteroperca microlepis occupy West Florida (WF), USA, estuaries as juveniles and have a spatially complex life cycle with ontogenetic habitat shifts and offshore spawning. We tested whether age-0 gag otolith stable isotope values distinguished WF nurseries and assessed isotopic variability at multiple temporal and spatial scales. Northern and southern juveniles had distinct otolith carbon (δ13C) and oxygen (δ18O) stable isotope values despite evidence of interannual variability, and both year-specific and combined year models had high (>80%) classification accuracies. We investigated long-term stability of otolith δ13C and δ18O by comparing age-0 gag collected during 2009-2012 and 2020-2021. The δ18O values of southern age-0 otoliths decreased over time, thus decreasing inter-regional differences and the classification accuracy of the combined year model (79%). Concomitantly, age-0 otoliths became depleted in 13C across regions, which may result from increased limestone dissolution (i.e. dekarstification) in the Floridan aquifer. We identified greater decadal variability in region-specific stable isotope values than has been documented in previous studies, indicating that a cohort-specific approach will likely be required to estimate gag lifetime movement.

Just Hitching a Ride: Stable Isotopes Reveal Non-Feeding Behaviour of Anisakis simplex Within Its Host Fish.

Anisakis simplex larvae, commonly found in marine fish, cause anisakiasis in humans, resulting in gastric to gastro-allergic symptoms. Despite known health risks, the impact of Anisakidae larvae on fish hosts is less understood. This study aimed to investigate this interaction by assessing the feeding strategy of A. simplex. Anisakis larvae were isolated from North Sea Merluccius merluccius tissues (stomach, body cavity, liver and muscle) and were analysed for carbon (δ13C) and nitrogen (δ15N) isotope values. Significant differences in δ13C values were found among host tissues, with the liver differing from muscle and stomach tissues. In contrast, no differences were noted for the associated parasites. Additionally, δ15N values indicated that the host occupied a significantly higher relative trophic position than its parasite. This suggests a lack of direct nutrient transfer from host to parasite, as the parasite would typically exhibit higher stable isotope values than the tissue they feed on. Therefore, A. simplex's stable isotope values might reflect those of its previous host (crustacean and/or small fish), providing insights into diet and movement of the paratenic M. merluccius host. Further research is needed to confirm these findings across different fish species and to explore A. simplex as a proxy for trophic ecology.

Isotopic analysis of modern sorghum and finger millet from different altitudes in Ethiopia: implications for ancient farming practices

C4 crops such as sorghum (Sorghum bicolor) and finger millet (Eleusine coracana) have played a significant role in the economic livelihood in arid and semi-arid zones of tropical and sub-tropical Africa since prehistoric times. However, to date, our knowledge of their past management practices is limited. Stable isotope analysis of archaeobotanical remains has been recognized as a valuable tool for reconstructing past agricultural practices, e.g. water management, and fertilization. Nonetheless, our limited understanding of the isotopic variability of C4 plants calls for further research on modern plant before application to archaeobotanical remains. In this paper, we aim to enhance our understanding of modern C4 botanical remains' isotopic variability by analyzing sorghum and finger millet plants. These crops were cultivated according to traditional local practices and collected from ten villages located in the Konso Zone (South Ethiopia) and Tigray Regional State (North Ethiopia), where they are among the daily ingredients for food, and traditional alcoholic and non-alcoholic drinks. We analyzed carbon and nitrogen stable isotopes of seeds and biosilica content in chaff, as it has been suggested that a relationship can exist between silicon and C:N. Carbon isotope values show significant variability, positively correlated with altitude. By demonstrating the sensitivity of C4 grain carbon stable isotope to altitude variations, which are likely connected to water availability, this study offers invaluable insights for the accurate assessment of isotopic values derived from ancient C4 crops. The absence of significant correlations with δ15N suggests that nitrogen isotope values may be less effective for understanding environmental variations in this kind of context. This highlights the limitations of nitrogen isotope data for interpreting ancient agricultural practices and underscores the importance of relying more on carbon isotopes for insights related to environmental conditions and altitude. Furthermore, we confirm that the amount of assimilated carbon may depend also on the biosilica content, which is in turn modulated by environmental parameters such as water availability or soil silicon levels.

The Paleocene‐Eocene Thermal Maximum Recognized in Distal Alluvial Fan Strata of the Sevier Fold‐And‐Thrust Belt (Southwestern Wyoming, USA)

AbstractFifty‐six million years ago a massive flux of exogenic carbon was rapidly released into Earth's oceans and atmosphere during the Paleocene‐Eocene Thermal Maximum (PETM). The warming associated with this release persisted for ∼200 kyr. It had severe impacts on ocean environments, global ecosystems, and the hydrologic cycle. Yet, regional patterns of response within continental settings are not well constrained. Here we describe the first recognition of the PETM in the Greater Green River Basin of western Wyoming, USA. We present new sedimentologic, chemostratigraphic, and paleontologic data from the Chappo Member of the Wasatch Formation in the Sevier fold‐and‐thrust belt. The Chappo Member contains lithofacies indicative of debris flows, ephemeral and incisional stream channels, and well‐drained overbank deposits, which, along with the geographic position of the study area, indicate a distal alluvial fan setting. Using pedogenic carbonates, we find a negative carbon isotope excursion (CIE) of ∼3.8‰ associated with the first appearance of Celtis endocarps stratigraphically above beds containing late Paleocene mammals. The CIE magnitude here is considerably smaller, compared to records from the Bighorn Basin, which we interpret to represent drier, better‐drained conditions. High baseline carbon isotope values suggest dry conditions in the study area, which likely resulted from well‐drained sediments associated with the distal alluvial fan. Low amounts of precipitation, as suggested by previous climate models, may have contributed to dryness. We also find sedimentologic evidence consistent with an enhanced hydrologic cycle during the PETM, as seen in other basins in the region.

Timing and origin of the Lomagundi-Jatuli Event: Insights from U[sbnd]Pb geochronology, C-O-Fe isotopes and REE compositions from the Jingshan Group, North China Craton

The Lomagundi-Jatuli Event (LJE) represents perhaps the largest and longest positive carbon isotope excursion of Earth history. However, the synchroneity, scale, and linkage of the LJE to Earth's early history of atmospheric oxygenation remain controversial. Strata of the Paleoproterozoic Jingshan Group of the North China Craton that preserve the isotopic record of the LJE excursion in marble layers and abundant graphite deposits provide an opportunity to elucidate the significance of the LJE. Carbon isotopic values (δ13CV-PDB) of the LJE based on analysis of 20 samples of the Lugezhuang Formation, lower Jingshan Group, range from −0.8 to +9.6 ‰ and display positive co-variance with stable oxygen isotope values (δ18OV-PDB). The positive carbon isotope excursion is constrained to 2140.6 ± 8.5 Ma (MSWD = 0.82, n = 25) based on magmatic zircon UPb geochronology of biotite granulite. Variation of facies-dependent carbon isotope values, the presence of graphite deposits of the Douya Formation, upper Jingshan Group, and the absence of a Ce anomaly in PAAS normalized REE patterns of marble samples suggest that the positive carbon isotope excursion is not linked to a marked increase of organic carbon burial and associated significant atmosphere oxygenation. Elevated concentrations of iron and PAAS-normalized middle REE enrichment of analyzed Jingshan Group marble samples point to anoxic and ferruginous oceanic conditions during accumulation of Jingshan Group carbonate. A positive Eu anomaly (average = 1.58), low La (average = 0.23), (Nd/Yb)N (average = 1.27), and Y/Ho (average = 36.6) anomalies, and negative iron isotope values (average δ56Fe = −0.12 ‰) are consistent with accumulation of Paleoproterozoic Jingshan Group carbonate in a restricted marine setting that was affected by high temperature hydrothermal fluids. Enrichment of the studied samples in heavy carbon isotope suggests elevated bio-productivity in the restricted, redox stratified marine setting in which Jingshan Group carbonate accumulated. Thus, it is likely that the positive stable carbon isotope excursion associated with Jingshan Group strata as well as other contemporaneous isotope excursions are local signals that are linked to a global perturbation of the carbon cycle.

Utilization of stable isotopes in teeth to investigate pygmy sperm whales (Kogia breviceps) in the southeastern United States

AbstractThe pygmy sperm whale (Kogia breviceps) is currently the second‐most stranded cetacean in the southeastern United States (SEUS), but information concerning their population structure is severely limited. This study used stable isotope analysis to investigate the isotopic niches and population structure of K. breviceps among three regions in the SEUS determined by the distance of the continental shelf break and a fourth region in the Gulf of Mexico. Teeth from stranded individuals were subsampled via dental drill at four separate areas on each tooth, representing four different age classes: calf, juvenile, subadult, and adult. Stable isotope ratios of carbon and nitrogen were measured in the organic component of 42 teeth, and oxygen isotope ratios were measured in the inorganic (hydroxyapatite) component of 19 teeth. No differences were found in δ13C, δ15N, or δ18O values between regions. However, differences between age classes were significant for adults and subadults for δ13C and adults and juveniles for δ15N. Differences between males and females were also significant for δ15N. Results from this study provide the first carbon and nitrogen isotope values from different age classes of pygmy sperm whales as well as the first reported oxygen isotope values for this species.

Carbon isotopic record of a platform-to-basin transect through the Permian Reef Complex (Guadalupian) in the Delaware Basin of Texas and New Mexico

The Guadalupian Permian Reef Complex of the Delaware Basin is one of the most studied carbonate reef systems of the Paleozoic. Despite extensive work on the carbonate sedimentology, sequence stratigraphy, and diagenetic history of the Delaware Basin, a high-resolution carbonate carbon isotope record along a platform to basin transect for the Capitanian (264.3–259.5 Ma, the youngest age of the Guadalupian Epoch) does not yet exist. The carbon isotopic record of the Delaware Basin is important because 1) it allows us to test hypotheses about controls on the carbon isotope proxy, 2) it provides constraints on how well modern carbonate platforms like the Great Bahama Banks serve as analogues for ancient carbonate settings, and 3) these types of restricted basins likely played an important role in Permian carbon cycling and the Capitanian extinctions.In this study we present 493 new Capitanian carbonate carbon isotopic values paired with a detailed sedimentological and sequence stratigraphic framework from the platform, slope, toe of slope, and deep basin of the Delaware Basin. The bulk of the new δ13C values fall within the range of previously reported unaltered carbonates from the basin, suggesting that these results record primary environmental processes and were not significantly altered by diagenetic overprinting. With this dataset, we test hypotheses about sources of carbon isotopic variability in shallow carbonate platforms. Our results indicate that in the Delaware Basin there are no systematic and resolvable depth or lateral gradients in carbon isotopic values, that δ13C values do not vary as a function of grain type, and that there is no resolvable relationship between carbon isotopic composition and sea level change. However, we do document statistically significant differences in δ13C distributions among facies associations which we attribute to the isotopic evolution of an upwelling water mass due to direct precipitation of mud along the slope. Our results support the idea that increasing carbon isotopic values through the Capitanian were driven by increased organic carbon burial in restricted basins.

How the vertical gradient of light in the understorey and water seasonality affect leaf traits of Vanilla phaeantha (Orchidaceae), a crassulacean acid metabolism (CAM) hemiephyte.

Structural and physiological leaf traits and their plasticity were compared in the hemiepiphyte Vanilla phaeantha . This species grows along a phorophyte reaching different understorey positions and exhibiting diverse responses to environment changes. We analysed three height strata above the ground, establishing a light gradient, and considering seasonal water fluctuations. The upper leaves had higher area and mass and were less pigmented. The dry season induced a reduction of approximately 2h of stomatal opening over the diel 24h crassulacean acid metabolism (CAM) cycle in the leaves at all understorey positions. The leaves more exposed to sunlight were larger with higher titratable acidity during the rainy season, while the leaves near the ground maintained the same rates of stomatal conductance and nocturnal acidification between seasons, with lowest values of carbon isotopes in the rainy season. Our research showed that some structural leaf traits (such as specific leaf mass, biomass, and saturated water content) are sensitive to variation in understorey position. In contrast, other physiological traits (stomatal conductance, transpiration, and fluorescence parameters) are more sensitive to seasonal variations. The results are a novelty in assessing the variation of CAM along the same plant in a height gradient and under field conditions.

Ash deposits link Oceanic Anoxic Event 2 to High Arctic volcanism

Oceanic Anoxic Event 2 (OAE 2) was a major environmental perturbation that occurred ∼94 million years ago. It is associated with profound changes in global climate and carbon cycling, which are commonly attributed to large-scale carbon release from large igneous province (LIP) volcanism. However, the specific LIP(s) involved and the mechanisms of carbon release remain poorly understood, as indicated by discrepancies between carbon release rates suggested by numerical models and LIP degassing estimates. Our study refines the eruptive history of the High Arctic large igneous province (HALIP) by dating ashfall deposits in marine sediments from the Canadian High Arctic using an integrated stratigraphic approach. Our results show that silicic HALIP volcanism began tens of thousands of years before OAE 2, suggesting a strong causal link. Volcanic activity coincides with a marked shift in carbon isotope values, linked to the degassing of HALIP magmas and/or thermogenic gas release. We propose that the concurrent activity of two LIPs—the HALIP and the Kerguelen Plateau—could account for the high rates of carbon release inferred for OAE 2, providing a hypothesis for its pervasive environmental impact.

Characteristics and Origin of Natural Gas in Yongfeng Sub-Sag of Bogda Mountain Front Belt

By systematically analyzing the natural gas composition, carbon isotopes, and source rock characteristics in the Yongfeng sub-sag of the Bogda Mountain front belt, natural gas characteristics were determined, and the genetic types and sources of natural gas were investigated. The research results indicate that methane is the main component of natural gas in the Yongfeng sub-sag, with low levels of heavy hydrocarbons and a high drying coefficient. These characteristics make it dry gas, which refers to natural gas with a methane content of over 95%. The ethane carbon isotope δ13C2 of natural gas is −28.5‰ and belongs to oil type gas. The methane carbon isotope δ13C1 of natural gas is −58.6‰~−59.4‰, has a relatively depleted methane carbon isotope value, shows significant differences from the surrounding natural gas methane carbon isotope, and belongs to the category of biogenic gas. The Permian Lucaogou Formation is the main source rock in the study area, with good organic matter abundance. The microscopic components of kerogen are mainly composed of sapropelic formations and the organic matter type is I–II1. The source rock has a high maturity and has reached the mature stage, mainly consisting of oil and wet gas. The ethane carbon isotope of natural gas in the Yongfeng sub-sag shows as oil type gas, which is consistent with the kerogen type of the Lucaogou Formation source rocks, indicating that the natural gas mainly comes from the Lucaogou Formation source rocks. Based on comprehensive data and information on natural gas composition, carbon isotopes, and burial history of the source rocks, it is believed that some of the crude oil generated from the Lucaogou Formation in the early stage underwent biodegradation due to tectonic uplift, resulting in biogenic methane and the formation of crude oil biodegraded gas.

Growth pattern and turnover of carbon and nitrogen measured by stable isotope ratios in the hair of sika deer (Cervus nippon).

Hair is known to preserve diet history and other physiological information during its growth period and is often used in chemical analyses. However, the growth patterns and turnover of hair vary according to the animal species or habitat, so understanding these patterns in the target animal is necessary for interpreting the results of hair analyses. In this study, we aimed to elucidate the growth pattern and dietary information of winter coat hair in captive sika deer (Cervus nippon). Experiments involving hair-staining and shaving were conducted to elucidate the growth pattern of sika deer hair. A diet-switching experiment was conducted to ascertain what dietary information is reflected in the carbon and nitrogen stable isotope values of the deer winter coat. Hair samples collected from each body site (head, shoulder, back, and hip) were analyzed using an elemental analyser interfaced with an isotope-ratio mass spectrometer. The winter coat grows from early September to early November, and then stops after that. During the growth period of the winter coat, the hair of the shoulder and back grew at a constant rate. The carbon and nitrogen stable isotope values of hair reflected the deer's feeding history during hair growth, but there seemed to be a time lag in the hip hair. The results suggest that the guard hair of the shoulder is suitable for hair analysis in sika deer. The obtained information on growth patterns and isotopic change of hair from captive sika deer according to diet be useful for interpreting the results of future analyses using hair samples of wild deer.

Highly enriched carbon and oxygen isotopes in carbonate-derived CO2 at Gale crater, Mars

Carbonate minerals are of particular interest in paleoenvironmental research as they are an integral part of the carbon and water cycles, both of which are relevant to habitability. Given that these cycles are less constrained on Mars than they are on Earth, the identification of carbonates has been a point of emphasis for rover missions. Here, we present carbon (δ13C) and oxygen (δ18O) isotope data from four carbonates encountered by the Curiosity rover within the Gale crater. The carbon isotope values range from 72 ± 2‰ to 110 ± 3‰ Vienna Pee Dee Belemnite while the oxygen isotope values span from 59 ± 4‰ to 91 ± 4‰ Vienna Standard Mean Ocean Water (1 SE uncertainties). Notably, these values are isotopically heavy (13C- and 18O-enriched) relative to nearly every other Martian material. The extreme isotopic difference between the carbonates and other carbon- and oxygen-rich reservoirs on Mars cannot be reconciled by standard equilibrium carbonate-CO2 fractionation, thus requiring an alternative process during or prior to carbonate formation. This paper explores two processes capable of contributing to the isotopic enrichments: 1) evaporative-driven Rayleigh distillation and 2) kinetic isotope effects related to cryogenic precipitation. In isolation, each process cannot reproduce the observed carbonate isotope values; however, a combination of these processes represents the most likely source for the extreme isotopic enrichments.

IN SITU STABLE ISOTOPE MEASUREMENTS IN FORAMINIFERAL TESTS BY SIMS

ABSTRACT Fossilized tests of foraminifera are arguably the most important archives of past climate, and many of the longest paleoclimate records have been compiled by the measurement of the oxygen and carbon isotope composition of foraminiferal tests collected from seafloor sediments. Since the analytical methodology was established in the late 1940s, multiple tests are pooled and analyzed, resulting in a single oxygen and carbon isotope value representing their mean composition. These records compiled by multi-test analysis provide, in most scenarios, a faithful picture of the Earth’s past climate. However, foraminiferal tests feature isotopic heterogeneity on micrometer scales and thus record a wealth of additional information that can be assessed by secondary ion mass spectrometry (SIMS) using spots of 10 µm or less. This paper provides a history of in situ stable isotope measurements in foraminifer tests by SIMS, discusses landmark studies, and offers an outlook on future research.

Stable carbon isotope evolution of formaldehyde on early Mars

Organic matter in the Martian sediments may provide a key to understanding the prebiotic chemistry and habitability of early Mars. The Curiosity rover has measured highly variable and 13C-depleted carbon isotopic values in early Martian organic matter whose origin is uncertain. One hypothesis suggests the deposition of simple organic molecules generated from 13C-depleted CO derived from CO2 photochemical reduction in the atmosphere. Here, we present a coupled photochemistry-climate evolution model incorporating carbon isotope fractionation processes induced by CO2 photolysis, carbon escape, and volcanic outgassing in an early Martian atmosphere of 0.5–2 bar, composed mainly of CO2, CO, and H2 to track the evolution of the carbon isotopic composition of C-bearing species. The calculated carbon isotopic ratio in formaldehyde (H2CO) can be highly depleted in 13C due to CO2-photolysis-induced fractionation and is variable with changes in atmospheric CO/CO2 ratio, surface pressure, albedo, and H2 outgassing rate. Conversely, CO2 becomes enriched in 13C, as estimated from the carbonates preserved in ALH84001 meteorite. Complex organic matter formed by the polymerization of such H2CO could explain the strong depletion in 13C observed in the Martian organic matter. Mixing with other sources of organic matter would account for its unique variable carbon isotopic values.

Isotope values reveal “canopy effect” in deer territoriality and maize consumption for dogs from archaeological sites in Kentucky dating to the Middle Woodland through Late Fort Ancient time periods

This research analyzes stable carbon, nitrogen, and oxygen isotope values in tooth collagen and enamel to investigate foraging and territorial behavior in white-tailed deer (Odocoileus virginianus Zimmermann) and maize (Zea mays Linneaus) consumption in dogs (Canis familiaris Linneaus). The study analyzed 22 deer teeth from 13 archaeological sites in Kentucky covering a span of approximately 1,500 years of human occupation. The article presents evidence of foraging and territorial behavior in white-tailed deer, identified through the “canopy effect” observed in deer stable carbon isotope values in remains spanning from the Middle Woodland (200 BCE – CE 500) to Late Fort Ancient (CE 1400 – 1680) time periods in Kentucky. Additionally, teeth samples from nine dog and one wolf (Canis lupus Linneaus) were analyzed and indicate significant consumption of maize in seven of the dog samples. These specimens came from seven archaeological sites in Kentucky dating from the Early through Late Fort Ancient (CE 1400 – 1680) time periods. The study also contributes to the growing database of isotope studies in the Eastern Woodlands by presenting carbon and nitrogen isotope values on deer bone collagen from nine deer bone samples from three of the same archaeological sites dating to the Middle Woodland to Early Late Woodland.

Characteristics and geological significance of carbon and oxygen isotopes of the Permian Lucaogou Formation dolomite in the southern Junggar Basin, northwestern China

Anomalously positive δ13C values in ancient dolomites are very rare. Dark gray argillaceous rocks of the lacustrine sediments of the Permian Lucaogou Formation are important source rocks in the Junggar Basin, and dolomites of varying thicknesses from 10 cm to 150 cm are often interspersed in argillaceous rocks. Based on the study of petrographic sections, this paper systematically analyzes the carbon and oxygen isotopes of dolomite and discusses the causes of abnormally high carbon isotope values and their significance in reconstructing paleoenvironment and paleoclimate. The results show that carbon isotope values are abnormally high in the dolomite of Lucaogou Formation, and the δ13C value is between +3.2 ‰ PDB and +19.6‰ PDB, with an average of +9.7‰ PDB. The δ18O values range from -17.4‰ PDB to -1.7‰ PDB, with an average of -8.1‰ PDB. From the lower part to the upper part of the Lucaogou Formation, the carbon isotope value gradually increases and becomes increasingly positive, and the carbon isotope of the dolomite deposited near the shore is more positive than that of the dolomite deposited far from the shore. The anomalously positive δ13C of the dolomite is mainly caused by microbial methanogenesis, with some contribution from evaporation. Microorganisms are mainly distributed at the redox interface. Evaporation controls the salinity and fluctuation of the redox interface in sedimentary water. The positive deviation difference in carbon isotopes between nearshore and offshore sedimentary dolomites may be related to the location of the redox interface during deposition. Together, the petrographic features and carbon and oxygen isotope signatures of the sections reflect the gradual evolution of the paleolake from a hydrologically open environment to a hydrologically closed one and the possible transition of the paleoclimate from a relatively warm to an arid condition, which is possibly a geochemical response to global climate change in the Permian period.

Modern history of hypoxia in Narragansett Bay: The geochemical record

Increased inputs of nitrogen from agricultural runoff, urbanization and suburbanization have resulted in degradation of water quality, including increased frequency and severity of hypoxia, in estuarine ecosystems. Much work has been conducted in recent years to characterize the spatial and temporal extent of hypoxia in coastal systems, but the historical record of hypoxia in such systems is much less well known. The current work examines the history of hypoxia in upper Narragansett Bay, an urbanized estuary in the northeastern U.S., through vertical profiles of geochemical markers in sediment cores. Concentrations of authigenic molybdenum indicate more frequent/ longer periods of hypoxia that are related to changes in population and anthropogenic inputs to the Bay from the surrounding watersheds. Cores from the urbanized upper bay, greatly affected by wastewater treatment facilities (WWTFs), indicate greater duration of hypoxia in the 20th century, with periods of hypoxia decreasing through mid-century and recurring thereafter. Trends of hypoxia are closely related to improvements and failures of WWTFs in surrounding communities. In Greenwich Bay, with a suburban watershed and only one WWTF, hypoxia increased substantially in parallel with growth of population in the surrounding watershed. Carbon and nitrogen concentrations and isotope values reflect increased nitrogen enrichment and productivity in the Bay in the 2nd half of the 20th century. These results can help inform study of the environmental responses to societal activities that may affect water quality.

Quantitative and Nuanced Approaches Elucidate Carbon Isotope Records

AbstractEarth scientists have leveraged carbon isotope records to interpret Earth history and establish chronostratigraphic frameworks for decades (e.g., Halverson et al., 2005, https://doi.org/10.1130/b25630.1; Kaufman & Knoll, 1995, https://doi.org/10.1016/0301‐9268(94)00070‐8; Knoll et al., 1986, https://doi.org/10.1038/321832a0; Saltzman & Thomas, 2012, https://doi.org/10.1016/b978‐0‐444‐59425‐9.00011‐1; Scholle & Arthur, 1980, https://doi.org/10.1306/2f91892d‐16ce‐11d7‐8645000102c1865d). Increasingly detailed and nuanced approaches have been applied to understanding carbon isotope records in light of local‐ and regional‐scale processes that complicate interpretations. The recent work of Gazdewich et al. (2024, https://doi.org/10.1029/2023gc011376) is a prescient example, in which they conduct a series of analyses to constrain the influence of authigenic carbonate burial on the global carbon isotope mass balance during the Late Devonian. Here, I briefly review some recent developments in quantitative approaches to understanding carbon isotope values measured from carbonate rocks (δ13Ccarb), with a focus on comparisons of measured δ13Ccarb values, models for understanding what controls δ13Ccarb values, and correlation tools for aligning δ13Ccarb stratigraphies. These new approaches are elucidating carbon isotope records across Earth history and may prove to be transformative for our understanding of the global carbon cycle.

Nutrient Shift in the Yucatan Basin during the late Early Miocene: Evidence from calcareous nannofossils and stable isotopes at ODP Leg 165 Site 998 Hole A

Paleoceanographic reconstructions in the Caribbean Sea during past climate transitions, namely the Late Oligocene to Early Miocene (up to the Miocene Climatic Optimum and Monterey Excursion) are crucial to understanding the effects of the Eastern Pacific interchange with the Atlantic Ocean. Studies of the planktonic domain in the Yucatan Basin during the Early Miocene are limited, with most Caribbean research focused on reconstructing the series of events that precede the final closure of the Isthmus of Panama in the Early Pliocene. Furthermore, paleoceanography of the Yucatan Basin is largely unrefined during this time, even though it is an important transition for ocean gateways, and development of Atlantic deepwater and Atlantic Meridional Overturning Current (AMOC), driving global ocean circulation. Here we conduct a relative percent abundance analysis of calcareous nannofossils and stable isotopes from bulk sediment of drill cores spanning the Upper Oligocene to Lower Miocene in the central Yucatan Basin, collected by the Ocean Drilling Program Leg 165 at Site 998 Hole A. Nannofossil assemblage data record a shift from a eutrophic to oligotrophic system ∼19.2–17.65 Ma. Eutrophic taxa (Reticulofenestra spp. and Cyclicargolithus floridanus) decline at ∼20.23 Ma, while oligotrophic taxa (discoasters and sphenoliths) increase as stable carbon isotope values decline. The palaeoecological turnover coincides with a possible restriction in the Central American Seaway (CAS) ∼20.7–21 Ma. Population dynamics of the Hole 998 A nannofossil assemblage track with global declines in C. floridanus relative abundance between ∼20.2 to ∼20.5 Ma, followed by a subsequent decrease in Reticulofenestra spp. These data suggest water mass stratification in the Yucatan Basin during the Early Miocene ∼19.2–17.65 Ma, likely due to restriction of the CAS.

Stable isotope spatial patterns for the Southwest Atlantic Ocean towards polar waters

Mapping stable isotope gradients (isoscapes) has become a powerful tool to understand and forecast the status and variability of marine ecosystems at different levels of ecological organization. To differentiate five marine areas from the Southwest Atlantic Ocean towards oceanic and polar waters, a key foraging area for many marine consumers, we built isoscapes at different spatial scales using carbon (δ13C) and nitrogen (δ15N) isotope values of phytoplankton, zooplankton and particulate organic matter in sediment. We analyzed the isotopic variability between marine areas in relation with oceanographic parameters (e.g. temperature, salinity) and geographical sampling site data (e.g. latitude, longitude). We collected samples during 6 oceanographic surveys conducted in spring and autumn between 2014 and 2019 at the Beagle Channel, the Atlantic coast of Tierra del Fuego and Burdwood Bank. We included also published isotopic data of zooplankton from two other oceanic areas (the Polar Frontal Zone and Polar Antarctic Peninsula waters) to construct large-scale isoscapes. We found that the marine areas analyzed have substantially different δ13C and δ15N baselines; some differences exist between spring and autumn but the general pattern of isotopic variability remains similar. Combining different biological components and spatial scale analysis, isotopic variability was found to be related to variables such as seawater temperature, depth, chlorophyll and nutrients. The generated data will enhance the efficacy of isoscapes in long-term monitoring initiatives that documents alterations in attributes and features across marine expanses. This is particularly pertinent to areas under legal protection, such as the oceanic Marine Protected Areas (MPAs) established in Argentine waters.